An ink jet printing method is a print process in which ink droplets are jetted and adhere to a recording medium, such as paper. With recent innovative advances in ink jet printing technology, an ink jet printing method has been used in the field of high-resolution printing, which was achieved only by silver halide photography or offset printing. Thus, an ink jet printing ink that can be used in ink jet printing to form glossy images equivalent to those of silver halide photography using high-gloss recording media, so-called special paper, comparable to photographic paper or art paper used in the field of silver halide photography or offset printing has been developed. Furthermore, even with plain paper, an ink jet printing ink that can achieve image quality equivalent to that of silver halide photography has been developed.
In recent years, with the spread of image forming technology using digital data, desktop publishing (DTP) has become increasingly common particularly in the field of printing. Even in printing in DTP, color proofs are prepared in advance to check the gloss and the color of an actual printed matter. An ink jet printing method has been used to output such proofs. Because color reproduction and stability reproduction of printed matter are required in DTP, special paper for ink jet printing is generally used as a recording medium.
Special paper for ink jet printing is designed to achieve gloss and color equivalent to those of outputs printed on actual printing paper. Thus, the quality of special paper is appropriately adjusted to the type of actual printing paper. However, manufacture of special paper corresponding to all types of actual printing paper will lead to high manufacturing costs. Thus, in color proof applications, there is a demand that ink jet printing be performed on actual printing paper rather than special paper. If proofs printed directly on actual printing paper rather than special paper by ink jet printing can be used as final proofs, proofreading costs can be reduced greatly. Synthetic paper formed of polyethylene resin or polyester resin blended with inorganic filler, widely used in the field of printing, has excellent recyclability and has received attention as an ecological material in recent years.
Actual printing paper is coated paper that includes a coated layer for receiving an oil-based ink on the surface thereof. However, the coated layer has a poor ink absorption ability. Water-based pigment ink, which is generally used in ink jet printing, therefore penetrates insufficiently into the recording medium (actual printing paper), causing blurring or uneven agglomeration in an image.
To address these problems, for example, Japanese Unexamined Patent Application Publication No. 2005-194500 (Patent Document 1) discloses a pigment ink that contains a polysiloxane compound as a surfactant and an alkane diol, such as 1,2-hexanediol, as a dissolution aid to reduce blurring and have a high gloss on special paper. Japanese Unexamined Patent Application Publications Nos. 2003-213179 (Patent Document 2), 2003-253167 (Patent Document 3), and 2006-249429 (Patent Document 4) propose that the addition of glycerin, a diol alcohol solvent, such as 1,3-butanediol, or a triol alcohol solvent, such as pentanetriol, to ink control the penetration of the ink to a recording medium, thus forming high-quality images.
In a previous patent application (Japanese Patent Application No. 2007-241158), the present inventors have proposed that the addition of a surfactant, such as polysiloxane, and a poorly water-soluble alkane diol, a water-soluble alkane diol, and an alkane triol as alcohol solvents to an ink provide high-quality images free of white streaks and harshness even in low-resolution printing on a recording medium having low liquid absorbency, such as actual printing paper.